Zn-rich coatings

ABSTRACT

PAINTS BASED ON ORGANIC TITANATE POLYMER BINDERS AND CONTAINING ELECTRICALLY CONDUCTIVE PIGMENTS, E.G., ZNC, CONT FOR THE PROTECTION OF STEEL WORK, ARE IMPROVED BY THE INCORPORATION OF AN ORGANIC ALIPHATIC TITANATE MONOMER SUCH AS BUTYL HEXYLENE GLYCOL TITANATE. THE PAINTS CAN BE APPLIED IN RELATIVELY THICK FILMS HAVING GOOD ADHERENCE AND RESISTENCE TO CRACKING.

nited States Patent Int. ci. (209a 5/10 US. Cl. 106-1 7 Claims ABSTRACTOF THE DISCLOSURE Paints based on organic titanate polymer binders andcontaining electrically conductive pigments, e.-g., zinc, for theprotection of steel work, are improved by the incorporation of anorganic aliphatic titanate monomer such as butyl hexylene glycoltitanate. The paints can be applied in relatively thick films havinggood adherence and resistance to cracking.

In the protection from corrosion of ferrous metals, e.g. steelwork, itis known to use paints based on inorganic binders and containing finelydivided metal particles, usually aluminium or zinc, as pigment. Suchpaints are desirable for protecting surfaces exposed to temperaturesabove about 250 C., for example exhaust flues, pipelines carrying hotliquids, chemical plant and cylinder blocks of internal combustionengines, as well as surfaces which remain at ambient temperatures.

For most such purposes it is desirable to use relatively thick coatingsof paint to provide good protection. It is known to base such inorganicheat-resisting paints on polymerized butyl titanate but in practicedifliculties have been encountered. Thus when high proportions ofmetallic zinc pigment are used, to provide a .so-called zincrich paintbased on butyl titanium polymer, a paint coating with inferiormechanical properties results, while with lower proportions of zincpigment the protection provided is insuificient.

It is moreover only practicable to apply such paints to substrates inrelatively thin coatings, as otherwise the defect known as mud-crackingappears whereby the coatings tend to lose adhesion and to peel.

Silicate-based paints are also available to protect steel work fromcorrosion. Silicate paints have the advantage over titanate paints ofbeing able to be applied as relatively thick coatings without crackingor peeling. However, silicate paints are not storage stable, and arecommercially supplied as a two-pack product for admixture before use.Moreover, the corrosion resistance of coatings of silicate paints is notalways satisfactory.

There is a need for a single-pack paint based on inorganic binders whichis capable of being applied in thick coatings having good adherence andgood resistance to corrosion.

The present invention provides a paint comprising electricallyconductive pigment, and a binder comprising a major proportion of analkyl titanate polymer and a minor proportion of an organic aliphatictitanate monomer. It has surprisingly been found that the presence of aminor proportion of an organic aliphatic titanate mon omer in the bindercan give rise to paints which can be applied in relatively thick fihnsof from 25 to 120 microns, generally from 40 or 80 to 100 microns,without mud-cracking.

The electrically conductive pigment preferably consists of metalliczinc. However, minor proportions of zinc dust may be replaced by otherconductive pigments, e.g. other metals, aluminium or graphite. Inparticular, up to 25% ice by weight of the zinc may be replaced bygraphite, e.g. ordinary flaked graphite or micronized grade graphite.Paints containing some graphite may have improved resistance to settlingon storage.

The electrically conductive pigment is preferably present in an amountof from to 92% by weight, particularly from 78% to 89%, on thenon-volatile content of the paint. The use of too little electricallyconductive pigment gives rise to coatings having inferior resistance tocorrosion. The use of too much electrically conductive pigment givesrise to somewhat underbound coatings which are liable to crack onflexing and may crack on ageing.

The proportion of binder is preferably from 6% to 25 by weight on thenon-volatile content of the paint. The proportion of alkyl titanatepolymer to organic aliphatic titanate monomer is preferably from 75 :25to 99:1, preferably from :20 to 96:4. The use of too little titanatemonomer gives rise to paints which are not ap preciably better than theunsatisfactory titanate paints previously known. The use of too muchtitanate monomer reduces the binding power of the binder.

The nature of the alkyl titanate polymer is not critical. Polymers ofbutyl titanate are available commercially, and are preferred for thatreason, although there is no reason why polymers of other alkyltitanates, e.g. hexyl or octyl titanate, should not be used. Alkyltitanate polymers may be prepared in one step by reacting titaniumtetrachloride with a mixture of water and the alcohol, the degree ofpolymerization being controlled by the amount of water present. Thepolymers may be characterized in terms of their Ti-O content. Suitablecommercially available grades of butyl titanate polymer have TiOcontents ranging from 27.6% to 36% by weight. These polymers are solublein the common organic solvents, e.g. ethyl alcohol and hydrocarbons.Polymers having TiO contents of up to about 60% by weight are generallysoluble in hydrocarbon solvents. Polymers having TiO contents aboveabout 50% may, however, show inferior adhesion to substrates. We preferto use a polymer having a TiO content of 34.1% to 35.0% by weight.

The organic aliphatic titanate monomer is a compound which does notcontain Ti-O-Ti linkages, and may be a titanate of an alcohol, a glycolor an alkanolamine. Each organic group may contain from 1 to 12 or morecarbon atoms. Titanates derived, at least in part, from glycols arepreferred. Mixed titanates may be used, for example, titanates ofalcohol/ glycol combinations. It is believed that the function of thetitanate monomer in the paint is dependent on its moderate rate ofhydrolysis in moist air, and that long chain glycols may hydrolyze tooslowly to be very effective. Suitable organic aliphatic titanatemonomers include the following, of which the first two are particularlypreferred:

Butyl hexylene glycol titanate. Octylene glycol titanate. Iso-octyltitanate.

Ethylene glycol titanate. Polyethylene glycol titanate. 2-ethylhexyltitanate.

Nonyl titanate. Triethanolamine titanate. Propylene glycol titanate.Polypropylene glycol titanate.

The paint is generally applied with the binder in solution in a volatileorganic liquid medium. The nature of this medium is not critical to theinvention. It is usual to use hydrocarbons, for example, toluene, xyleneor mineral turpentine, but polar solvents, e.g. aliphatic alcohols andether alcohols, may be useful, in conjunction with montmorillonitederivatives, to reduce settling on storage. Because the titanatematerials present tend to gel in the presence of water, the paints areformulated and stored under substantially anhydrous conditions.

that with butyl titanate a 60% to 70% loss of butyl radical occurs onexposure of the paint in the form of a thin film.

The compositions of this invention find especial usefulness as primingpaints for iron and steel, and offer long- The corrosion resistance ofthe paints may be improved term protection. If it is desired to overcoatthem with by the incorporation of mica, in an amount of from 0.1% moreconventional types of paint compositions, for examto 15%, preferably2.8% to 12%, by weight on the weight ple for providing a selected color,overcoating paints of of the electrically conductive pigment. known typebased on chlorinated rubber, vinyl or epoxide As additives to assistsuspension of the pigment on resins are preferred. storage and preventcracking, there may be added mont- The following examples illustrate theinvention. mor1llon1te derivat ves, e.g. that available as bentone, andEXAMPLE 1 ethyl cellulose derivatives. The use of anti-settling agentsis widespread in this type of paint. Butyl titanate polymer (containing35% to T10 8.09

There may also be included in the paint from 0.1% to Butyl heXyleIleglycol tltallate (comalmng 27% 5%, e.g. from 0.5% to 3%, by weight onthe non-volatile 2) content of the paint, of an organic silane. Suchsilanes Z11 1C Plgment 60-71 can help to improve adhesion and resistanceto fire and Mlea P cracking. Suitable silanes include alkyl alkoxysilanes, for Mommel'lnonlte del'lvatlve example methyl trimethoxysilane. Aromatle hydrocarbon Solvent 26-93 The paint may also includesuch other pigments, fillers, extenders, antioxidants and additives asmay be desired. 100-00 The paints are prepard by mixing the ingredientstogether in known manner to provide a single-pack storage- Welght Pgallon 20-24 Stable composition Non-volatile content (as deposited),percent 73.02

As already Plentioned the P of the illVeIl' When applied in the mannerhereinbefore described as U011 are especlally useful ProteetlngSubstrates P a coating on a prepared steel panel and submitted to theT0113 Petals, Steel, to f y ey be PP y ASTM Salt Fog Test the coatingwas still in good condibr115h 1ng p y addltlonal 0rga 11 1e SolventPelng tion after 5 weeks. In contrast, another paint, otherwise used 1fneeessal'y to reduce the pq f t0 Sultable similar, in which the zincpigment content was reduced to Y- The Surface before applleatlen 0f the85%, exhibited poor corrosion resistance under the same positions mustbe Well-cleaned. In the case of steel, after test di i rerfiovgl o5 cgiland gfiease the sgrface shouldalbe subgltan- EXAMPLES 2 To 21 tia y eerom oxi ation pro uct, prefera y by astcleaning, after which thecomposition should be applied The fprmulatlons of the palms Examples 2to 21 are as Soon as Possible set out in Table I below, figures beingbased on the total The compositions after application become cured and fgi gggf g g 3 s f ra ed on to hardened through chemical interaction withatmospheric 6 pam S p S e e P Y moisture, during which process organiccomponents of gnt'blasted steel test j m the.form of coatmgs from thetitanates, especially butyl alcohol, become freed and 40 to mlcronsthlck' Propemes the co'fmngs are are largely lost from the coating byevaporation set out m Table 11 below, where ratings are given on a Inthe field of electrically conducting paints, it is cusscale rangmg 2 0for g g? to 10 for Perfect tomary to express the proportion ofconductive pigment Performance Exposure watere means that as apercentage of the cured film, assuming complete recoated-Panels woutdoors at angle of moval of organic materiaL Owing to uncertainty asto 45 to receive maximum sunlight and sprayed w1th town water how muchorganic material is in fact lost, how at regular Intervalsmuchatmospheric moisture is absorbed by the vari- Key to Table ,1 oustitanates present, and to what extent the zinc becomes oxidized duringexposure, such expressions may not be BHGT Buty1 hfixylene glycol manaterealistic when applied to the present compositions. It has Y tltanatetherefore been preferred to express the conductive pigy heXYI tltane-temerit as a percentage of the non-volatile content of the NT-Nony1 tlta ae paint as deposited. As a rough guide, however, it appearsTTTri-ethanolamme titanate TABLE I Example 2 3 4 5 6 7 8 9 10 11Butyltitanate polymer percent) ian c r 131171 1 1313 61 1 1311 61BH7G4'I8 1311 61 1 1311 6. 1" BHE? 1311 6 5 311 GT Afiphatic mamapercent) 0. 37 0.43 0.41 1.41 1.50 0.46 0.43 1. 49 1.57 0.33 Hydrocarbonsolvent (wt. percent)... 24. 57 23.74 22.42 22.43 23.75 24.90 23.5723.57 24.91 24.76 Mica (wt. percent) 1. 74 0. 6. 14 6. 14 0. 65 0. 635.97 5. 97 0. 63 i. 74 Bentone (Wt. percent) 1. 74 1. 68 1. 59 1. 59 1.69 1. 77 1. 68 1. 68 1. 77 1. 73 Zinc dust (wt. percent)--- 62.66 64.9661.37 61.37 64.95 63.27 59.36 59.36 63.27 62.66 Graphite (wt. percent)Wt. percent zinc dust onnon-volatile material 83.1 85.2 79.1 79.1 85.284.2 78.3 78.3 84.3 83 1 Wt. percent titanate monomer on titanatepolymer- 10. 3 5 5. 1 20 20 5. 1 5 20 20 10. 4 Wt. percent mica on zinc2. 8 1 1O 10 1 1 10 10 1 2. 8 Wt. percent mice and graphite 011 zine 2.8 1 10 10 1 1 10 10 1 2. 8

Example 12 13 14 15 16 17 i3 19 20 21 B y titanete p y P g BH8GT manatepercent) 1.49 0.43 1. 49 0.43 1. 49 0.43 1.49 0.43 1.72 1.35 Hydrocarbonsolvent (wt. percent) 23. 56 23.56 23. 56 23. 56 23. 56 23. 56 23. 5623. 56 27.13 21.51 Mica (wt. percent) 5. 99 5. 99 5. 99 5. 99 5. 99 5.99 5. 99 5. 99 0. 0. Bentone (wt. percent)- 1. 66 1. 66 1. 66 1. 66 1.66 1. 66 1. 66 1. 66 1. 92 2. 07 Zinc dust (wt.percei1t)-- 59. 36 59.8659. 86 59. 36 59.36 59.36 59.86 59.36 55.24 29.54 Graphite (wt. percent)4. 66 5. 03 Wt. percent zinc dust on non-volatile matena 78. 3 78.3 78.3 78. 3 78.3 78. 3 78. 3 78.3 75. 90 75.90 Wt. percent, titanate monomeron titanate polymer- 20 5. 1 20 5 20 5. 1 20 5. 1 20. 06 20. 06 Wt.percent mica on zinc 10 10 10 10 10 10 10 10 1. 26 1. 26 Wt. percentmice and graphite on 21116.. 10 10 10 10 10 10 10 10 9. 7 9. 7

TABLE II Salt fog, 8 weeks, ASTM B117 Exposure, 45 watered BustingBlister microcrack Example Face Scribe Face Scribe 4 months 3% months 87 10 7 4% 9 75,6 7 10 a l3 2 2; at 2 6 4 10 6 1 10 We claim:

1. In a paint comprising (a) electrically conductive pigment in aproportion of from 75% to 92% by weight based on the nonvolatile contentof the paint, said electrically conductive pigment comprising at least75% by weight of metallic zinc, and

(b) a binder in a proportion of from 6% to 25% by 'weight based on thenon-volatile content of the paint, said binder comprising an alkyltitanate polymer containing up to 50 percent TiO the improvementcomprising, as a component of said binder, a monomeric titanate ester ofat least one member selected fromthe group consisting of alcohols,glycols and alkanolamines of 1 to 12 carbon atoms in a weight ratio ofpolymer to ester from :25 to 99:1.

2. A paint as claimed in claim 1, wherein the electrically conductivepigment is present in a proportion of from 78% to 89% by weight based onthe non-volatile content of the paint.

3. A paint as claimed in claim 1, wherein the alkyl titanate polymer isa butyl titanate polymer.

4. A paint as claimed in claim 1, wherein the titanate ester is a butylhexylene glycol titanate or an octylene glycol titanate.

5. A paint as claimed in claim 1, wherein there is also present from0.1% to 15% by weight on the weight, based of the electricallyconductive pigment, of mica.

6. A method of protecting a ferrous metal, which comprises applying tothe ferrous metal a coating, from 25 to microns thick, of the paintclaimed in claim 1.

7. A ferrous metal having a coating derived from the paint claimed inclaim 1.

References Cited UNITED STATES PATENTS 2,058,844 10/1936 Vaughn l0638.23,442,824 5/1969 Chandler ll7135.1 3,469,071 9/1969 Feldt et a1.117l35.1

LORENZO B. HAYES, Primary Examiner US. Cl. X.R.

